The present invention is directed to devices that regulate the flow of electric current and their fabrication methods. More specifically, the present invention is directed to Schottky-barrier source and/or drain transistors.
An electric current flow regulating device such as semiconductor device 100 (for example a transistor), seen in prior art FIG. 1, may include a silicon substrate 110, with an impurity doped source 120 and impurity doped drain 130. Source 120 and drain 130 are separated by a channel region 140. Atop the channel region 140 is an insulating layer 150. Insulating layer 150 typically consists of silicon dioxide, which has a dielectric constant of 3.9. A gate electrode 160, made from electrically conductive material, is located on top of the insulating layer 150.
When a voltage VG is applied to the gate electrode 160, current flows between the source 120 and drain 130 through the channel region 140. This current is referred to as the drive current, or ID. For digital applications, a voltage VG can be applied to the gate electrode 160, to turn the semiconductor device 100 “on.” In this state, the semiconductor device will have a relatively large drive current, ideally limited only by the resistance of the channel region 140. A different voltage VG can be applied to the gate electrode 160 to turn the semiconductor device 100 “off.” In this state, the ideal leakage current is zero. However, in practical applications, the drive current in the “on” state is not ideal because of parasitic impedances associated with other parts of the semiconductor device 100. For example, the source and drain regions have a finite impedance, resulting in a parasitic impedance which adds to the resistance of the channel region. Also, in practical applications, there is a certain finite amount of leakage current when the semiconductor device is “off.”
In prior art current regulating devices, the drive current is linearly proportional to the dielectric constant K of the insulating layer 150, and linearly inversely proportional to the thickness Tins of the insulating layer 150. The drive current ID is approximated by the relationship:ID˜K/Tins where K is the dielectric constant of the insulating layer and Tins is the thickness of the insulating layer.
One consideration in the design of current regulating devices is reducing the amount of power required to achieve a desired drive current. One way to reduce power consumption is by using a metal source and drain and a simple, uniformly implanted channel dopant profile, as described in U.S. patent application Ser. No. 09/465,357, filed on Dec. 16, 1999, entitled “METHOD OF MANUFACTURING A SHORT-CHANNEL FET WITH SCHOTTKY BARRIER SOURCE AND DRAIN CONTACTS” (now U.S. Pat. No. 6,303,479) and U.S. patent application Ser. No. 09/777,536, filed on Feb. 6, 2001, entitled “MOSFET DEVICE AND MANUFACTURING METHOD” (now U.S. Pat. No. 6,495,882), the contents of which are hereby incorporated by reference; these two patents have the same assignee as the present patent application.
Another consideration in the design of current regulating devices is the manufacturability. One way to improve the manufacturability of current regulating devices having gate insulators with high dielectric constant materials is to form the source and drain electrodes using a low temperature process such as that used for formation of Schottky or Schottky-like source and drain electrodes, as described in U.S. Provisional Patent Application 60/381,320, filed on May 16, 2002, entitled “LOW TEMPERATURE SOURCE AND DRAIN FORMATION PROCESS STEPS FOR THE MANUFACTURE OF MOSFET DEVICES,” the contents of which are hereby incorporated by reference.
There is a need in the art for a device for regulating the flow of electric current, which exhibits an improved drive current in the “on” state. There is a further need in the art for a method of manufacturing such a device at reduced temperatures.